Flame and burn resistant butadiene resin compositions

ABSTRACT

TETRABROMOBENZENE STRONGLY INHIBITS FLAMMABILITY AND BURNING OF POLYBUTADIENE RESINS.

3,786,087 FLAME AND BURN RESISTANT BUTADIENE RESIN COMPOSITIONS Wendell R. Conard, Kent, Ohio, and Ronald M. Ellis,

Evanston, Ill., assignors to The Firestone Tire 8: Ruhber Company, Akron, Ohio No Drawing. Filed Oct. 26, 1971, Ser. No. 192,476 Int. Cl. C081? 29/08; C09k 3/28 US. Cl. 260-415 A 6 Claims ABSTRACT OF THE DISCLOSURE Tetrabromobenzene strongly inhibits flammability and burning of polybutadiene resins.

FIELD OF THE INVENTION This invention relates to the flameand burn-proofing of butadiene polymer and copolymer resins (both hereinafter designated polybutadiene resins) by the incorporation therein of 2,3,5,6-tetrabromobenzene (hereinafter referred to simply as tetrabromobenzene). The products are particularly suitable for electrically insulating structural members where a combination of good electrical properties, fireand flame-resistance, mechanical strength, and resistance to heat-distortion are necessary.

BACKGROUND OF THE INVENTION Polybutadiene resins, particularly those having, in uncured state, a high proportion of the butadiene units incorporated in 1,2-configuration, have come into considerable use, particularly as electrically insulating structu'ral elements, due to their excellent mechanical and electrical properties. Such applications often require further a high degree of flameand burning-resistance; however, these properties are not easily achieved in this particular class of resins. Most conventional organic flameresistance-imparting materials which might be incorpo rated into such resins are either incompatible, ineffective in the amounts which are tolerable, or (what amounts to the same thing) must be used in such large proportions as to adversely affect the physical and/or electrical properties of the products. Of the inorganic flame-resisters, antimony oxide (Sb O is an effective agent; however it is expensive, and the principal sources thereof are unreliable. Phosphate compounds are helpful but by themselves are inadequate.

The tetrabromobenzene employed in this invention has heretofore been incorporated into polyester, polystyrene and polyurethane resins (British Pats. 1,079,984; 1,100,- 605 and 1,107,283; Reinforced Plastics (London) 11 (12), 357-60 (1970). However, it does not appear ever to have been employed in a context entailing the problems encountered with the butadiene-based resins involved in the present invention.

Accordingly, it is an object of the invention to provide a novel and effective flameand burning-resistant system for the polybutadiene resins.

Another object is to provide such a system which will eliminate dependence upon the expensive and procurement-vulnerable antimony oxide, or alternatively to reduce such dependence.

United States Patent O SUMMARY OF THE lNVENTION The above and other objects are secured, in accordance with this invention, in compositions comprising:

Parts by weight Polybutadiene resin 100 2,3,5,6-tetrabromobenzene 8-35 Adjuvant fiameand burning-resistance agents (phosphates, hydrated alumina, etc.) 0-30 1 Preferably 10-20.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polybutadiene resins These may be any resins which are based on polymers of butadiene or copolymers of butadiene with up to based on the copolymers, of styrene. Also minor proportions, say up to 15% basedon the copolymer of other ethylenically unsaturated compounds may be incorporated in the copolymers. These resins are usually prepared by (co) polymerizing the monomers by means of free radical or cationic catalysts to a relatively low molecular weight, say 1000-200,000, so that they are of at least a fiowable consistency. These low molecular weight (co) polymers are then incorporated with any desired fillers, reinforcing fibers or fabrics, pigments, etc. (including in case of the present invention, the tetrabromobenzene and/or adjuvants), peroxide or other curing agents if desired, etc.,

and the composite is cured under heat and pressure to produce the desired finished article.

More particularly, there have recently been developed a class of polybutadiene resins having at least 40%, and' preferably at least 60% by weight, of butadiene in the polymer molecule, and having at least by weight of the butadiene therein in the vinyl type of butadiene repeating unit structure. The average molecular weight (determined by intrinsic viscosity measurement) is at least 12,500 and the molecular weight distribution is such that at least 50%, and preferably of the polymer has a molecular weight above 10,000 and at least has a molecular weight above 2,000. It has been found that the presence of higher proportions of lower molecular weight polymers than allowed by these limitations causes slow curing rates and poor physical properties in the 3 polymer, approximately 0.5-6 parts, and preferably 1.5- 3.0 parts, by weight of dicumyl peroxide (or an equivalent weight of any other peroxide giving radicals of the structure R (CH )CO Where R independently in each occurrence represents a hydrocarbon radical of l-20 carbon atoms), and heating the polymers, usually under pressure. The curing temperature is advantageously at least 250 F. (120 C.), preferably about 300'350 F. (ISO-180 (2.). Generally, no advantage in the process or product is obtained by exceeding a temperature of 420 F. (215 C.). Obviously, the higher the temperature the shorter will be the curing time required. Generally at 350 F. (180 C.) a satisfactory cure is obtained in less than four minutes, and in some cases even within a few seconds. Cure times of more than four minutes usually provide no added advantage. Where fast cures are desired it is necessary to use a filler to avoid crazing or cracking. A filler, such as silica, is advantageously used in the proportion of 25-65, preferably 40-60 volume percent based on the combined resin-fil1er composition. Also the resins may be incorporated with glass fiber, either as chopped filler or else as glass fabric in a laminate, in which case the glass fiber will serve the purpose of a filler in preventing crazing and cracking on fast cures.

The adjuvant anti-flame and anti-burning agents The tetrabromobenzene may be used as the sole antiflame and burning agent in the practice of this invention, and, as the proportions thereof are increased, will provide fiameand burn-resistance in increasing degree up to any reasonably demanded level. This is a very considerable advantage, since many other agents are either expensive and/or not reliably available, as for instance is the case with combinations of antimony trioxide with halogen compounds, the most effective flame-resisting systems heretofore developed. However, these other conventional anti-flame agents may be used along with the tetrabromobenzene and, for any given level of flame-resistance required for the end use, will permit a reduction in the amount of tetrabromobenzene required for that given level of flame-resistance. In certain cases, a synergistic effect has been observed between the tetrabromobenzene and other flame-resistant agents so that the introduction of the other flame-retardant agent will permit a disproportionate reduction of the amount of tetrabromobenzene required for a given level of flame resistance. This disproportionate reduction will be observed up to a replacement of as much as 50% of said required amount of tetrabromobenzene. Such synergism has been observed in the case of hydrated alumina (2Al O -3H O).

The flameand burning-resistant compositions of this invention may be incorporated with any of the conventional glass, cellulosic or other reinforcing fabrics and fibers, and with any of the usual pigments, fillers and the like. These components do not substantially affect the flame resistance, but they do affect the physical and mechanical properties of the cured articles made therefrom. The tetrabromobenzene, in the amounts used in the practice of this invention, does not detract significantly from the physical, mechanical, thermal or electrical properties of the finished cured articles.

With the foregoing general discussion in mind, there are given herewith detailed examples of the practice of this invention. All parts and percentages givenare by weight.

EXAMPLE I High 1,2-polybutadiene resin solution 1 grams 2 220 Hexane ml 100 Silica (325 mesh) grams 380 Tetrabromobenzene do.... 3 -l5 Dicumyl peroxide mixture (40% active) do 45% solution in hexane of a. butadiene homopolyrner: 90% of butadiene units in 1,2-configuration; molecular weight parameters, Mw:29,000, Mn=23,000, DSV:0.3.

= 100 grams dry resin.

3 Per Table I.

A series of compositions was made up in accordance with the above recipe, varying the tetrabromobenzene from run to run as indicated in Table I. In each run, the ingredients, in the order listed, were mixed together in a planetary mixer. When the materials had become homogeneously mixed together, the batch was spread out in a tray, air-dried at 25 C. for 24 hours and then vacuum dried for an additional 24 hours at 0 C. Test plaques 6" x 6" x 0.1" were then molded in a laboratory press at 350 F. for five minutes under a total load of twenty tons normal to the faces of the plaques. Rockwell hardness and burning resistance ratings according to ASTM- D-635-68 were determined for the several specimens and are set forth in Table I.

1 Slower.

The critical figure is the burning distance, and it will be seen that Runs 2 and 3, using tetrabromobenzene, showed negligible values of this figure, which is highly desirable. Burning time is the time required for the fiame to spontaneously be extinguished; shorter burning times are desirable. Also the vertical burning time (as distinguished from burning time) of 163 seconds for Run No. 2 indicates a slower rate of burning in comparison with Run No. 1; in the vertical burning time test, the time is measured until the specimen is completely consumed, hence for this test increased vertical burning time is desirable (other results being satisfactory), since this reflects a slower burning rate. These comments, of course, apply also to the results set forth in Tables II-IV hereinbelow.

EXAMPLE II Blends containing polyethylene High 1,2-polybutadiene resin solution (as in Example I) grams 1 220 Hexane ml Polyethylene (Microthene', a product of U.S.I.

Co.) grams 2O Silica (325 mesh) do 380 Antimony trioxide do 2 0-5 Tetrabromobenzene do 2 0-15 Dicumyl peroxide mixture (40% active) do 10 1 100 grams dry resin.

Per Table II.

A series of compositions was made up in accordance with the above schedule, varying the tetrabromobenzene and antimony trioxide from run to run as set forth in Table II. The compositions were cured and evaluation in accordance with the procedure and testing of Example I. Set forth herewith in Table II are the results of the several runs.

Again it will be seen that the use of tetrabromobenzene in Runs 5-7 reduced the burning time and distance. The additional use of antimony oxide in Run 7 does not appear to have made any significant difference. A desirable increase in vertical burning time will be noted at the higher levels of tetrabromobenzene (Runs Nos. 6 and 7).

EXAMPLE III Butadiene/styrene copolymers High 1,2-butadiene/styrene copolymer resin 45 weight-percent solution in hexane of a copolymer of 60% butadiene, 40% styrene; 90% of butadiene units in cisconfiguration. DSV:0.33.

2 100 grams dry resin.

Per Table III.

A series of compositions was made up, cured and tested in accordance with the above schedule, using the procedure of Example I. Following are the results from the several runs.

heavy loading of alumina, it was necessary to apply the ignition flame for a much longer time (ignition time) than the seconds specified in the ASTM-D-635-68. This excessively long application of the ignition required to start burningcaused volatilization of a portion of the tetrabromobenzene, invalidating the remaining results.

EXAMPLE 'V Butadiene/ styrene copolymer alumina adjuvant High 1,2-butadiene/styrene copo lymer resin solution (as in Example III) grams 1 220 Alumina (as in Example IV) do.. 220 Silica glass do 80 Tetrabromobenzene do 0 or 20 Dicumyl peroxide mixture (40% mixture) grams.-- 10 1 100 grams dry resin. 2 Per Table V.

Two compositions were prepared and cured in accordance with the procedure of Example I, one with, and

TABLE III Run number s 9 10 11 12 13 14 Ingredients (grams):

'Ietrabromobenzene 0 0 20 20 20 20 30 Glass fiber 40 0 40 40 40 0 0 Atomite 180 220 180 170 160 220 220 Antimony trioxide 0 0 0 10 0 0 0 Zinc borate 0 0 0 0 20 0 J 0 Properties:

Rockwell hardness (Eseale) 51 02 42 43 48 47 '40 Ignition time (seconds) 30 30 30 30 30 30 Burning time (sec0nds) 591 433 66 81 61 57 48 Burning distance (inches) 4.0 3.0 0.00 .00 .00 .04 0 Vertical burning time (seconds) 176 189 229 203 266 210 211 Again the use of tetrabromobenzene (Runs 10-14) one without, the tetrabromobenzene. The results are set will be seen to result in negligible burning distance. The sample containing antimony trioxide was actually poorer than its control (Runs 11 vs. Run 10). The zinc borate (Run 12), however, shows definite benefit. Again, the mixtures containing tetrabromobenzene (Nos. 10-14) show enhanced vertical burning time.

EXAMPLE IV Alumina adjuvant High 1,2-polybutadiene resin solution (as in Ex- 1 Per Table IV.

A series of compositions was made, cured and tested, varying the ingredients as indicated in Table IV and using the procedure of Example 1. Following are the results:

TABLE IV Run number. 15 16 17 18 Constituents:

'letrabromobenzene (grams) 0 10 15 15 Thermogard B (grams) 0 0 0 5 Properties:

Rockwell hardness (E-sca1e).- 63 62 67 14 Ignition time (seconds)--- 80 103 129 180 Burning time (seconds)... 72 97 83 53 Burning distance (inches) 0 0 0 0 Vertical burning time (seconds).. 0 0 0 231 It will be noted that the ignition time was greatly increased by the tetrabromobenzene (Runs 16-18) so that they would be classified non-burning under ASTM- D- 635, a very desirable result. On account of the rather forth herewith in Table V.

TABLE V Run number 19 20 'Ietrabromobenzene used (grams) 0 20 Properties:

Rockwell hardness (E-scale) 63 Burning time (seconds) 398 71 Burning distance (inches) 2. 67 0. 04 Vertical burning time (seconds) 199 238 What is claimed is: 1. A peroxide cross-linked fiameand burning-resistant composition comprising Parts A butadiene resin 100 2,3,5,6-tetrabromobenzene -1 5-35 said butadiene resin prior to cross-linking being characterized by Percent of butadiene units in 1,2-

configuration At least Average molecular weight 12,500-55,000 Percent of polymer having molecular weight above 2000 At least Percent of polymer having molecular weight above 10,000 At least 90 Dilute solution viscosity 0.l9-0.7

2. A composition according to claim 1, wherein the composition contains from 10 to 25 parts of 2,3,5,6-tetrabromobenzene per parts of resin.

3. Composition according to claim 1, which further contains up to 30 parts of zinc borate as an adjuvant flame-resister.

4. Composition according to claim 1, which further contains up to 30 parts of hydrated aluminum oxide as 7 an adjuvant flame-resister.

5. A glass fiber reinforced article having a matrix of the cured resin of claim 1.

References Cited UNITED STATES PATENTS C'arothers 260-33.8 Asadorian 260-650 Gouinlock, Jr. 260-45.75 Gable 260-29.1 Parris et a1. 260-85.3 Willersinn et a1. 260-2.5 Birkner et al. 260-2.5

Schaifhauser et a1. 260-94.7

8 Lister et a1 2602.5 Macdowall 260-2.5 Gray et a1. 2'60-41 Green 260-2.5 Humphrey 117-138 Raley, Jr. 2'602.5

DONALD E. CZAJA, Primary Examiner R; A. WHITE, Assistant Examiner US. Cl. X.R.

260-45.7 R, 45.75 R, 94.7 A

mg UNITED STATES PATENT OFFICE CERTIFECATE @F CGRRECTION Patent NO- 5,786,087 Dared a y/ 5, 97

' i t fl JENDFTJL R. CONARD and RONALD N. ELLIS It is cerrified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 1 Line 54, after "1970" there should be a double parentheses --))'r.

in Column 4', Line 8, "0C, '7' should be 7090.,

In Column 4, Lire 56, evaluation should be --evaluated--. In Column 5, Line 58, "Runs" should be --Run-- In Column 5,, Example IV, Line 46, the first occurrence,

' "200" should be --220--.

.S igped and, sealed this 19th day of November 1974.

(SEAL).

Attest MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents 

